What does the disguised Rosalind promise to do for Orlando in As You Like It?
The answer to your question can be found in Act III scene 2 of this hilarious play, that examines the nature of love and in particular the stereotypes of lovers and how we love. Rosalind, having discovered Orlando's poem that he has written about his love for her hung up in the Forest of Arden, decides to engage Orlando directly in her disguise as Ganymede. She gains the truth from him that it was he that wrote the poem, and then goes on to tell Orlando how she managed to "cure" another man from the "madness" of love by "counsel":
He was to imagine me his love, his mistress, and I set him every day to woo me. At which time would I--being but a moonish youth--grieve, be effeminate, changeable, longing and liking, proud, fantastical, apish, shallow, inconstant, full of tears, full of smiles; for every passion something and for no passion truly anything, as boys and women are for the most part cattle of this colour...
At the end of this important scene, Rosalind promises to do the same for Orlando if he will do the same: imagine Ganymede to be Rosalind and come every day to woo him. The irony of this is keen and biting and also sets us up for how Rosalind is able to "train" her lover, disabusing him of his romantic and unrealistic notions, before revealing her identity to him.